Method of manufacturing electrode foundation structures



July 2, 1946. H, B LAW 2,403,225

METHOD OF MANUFACTURING ELEGTRODE FOUNDATION STRUCTURES Filed April 29, 1945 Ely. 7.

NVENTOR H n P@ LD E). LH Lu RNEY Patented Julyl 2, 1946 METHOD F MANUFACTURING ELECTRODE FOUNDATION STRUCTURES Harold B. Law, Princeton, N. J., assigner to Baillo Corporation of `America.,

Ware

a corporation of Dela- Application April 29, 1943', Serial No. 485,048

- 7 Claims.

1 My invention relates to television transmitting tubes and electrode structures and` more particularly to improved methods of manufacturing target structures suitable for use in tubes of the low velocity electron beam scanning and electron image types. l

In my prior application SerialNo. 463,065, filed October 23, 1942, of which this application is a continuation-impart, I described a target ,electrode wherein an imperforate sheet of vitreous material was provided with a great number of recesses, the sheet being etched to provide a corresponding number of apertures which might be used as image grid apertures or filled with conductive material to form a mosaic electrode. Ink

my prior structure the recesses or apertures as formed were nonuniformly distributed over the surface of the foundation sheet. This offered a disadvantage in that without a symmetrical array of recesses or apertures the degree of resolution obtainable when sucha target is used in a television tube is not as high as desired and cannot be maintained uniform from tube to tube.

It is an object ofmy invention to provide target structures for electronfbeam tubes such as of the television transmitting Vtype whereby higher sensitivity and lower distortion than those o btainable with prior structures may be obtained. It is a further object to provide a method whereby such structures may be lmanufactured with ease and at low cost. It is a further object of`v my invention'toprovide methods kof manufacturing lelectron beam targets having a uniform array of discrete mosaic areas, and it is a still further object to provide a. target elect-rode and method of manufacture which maybe duplicated with a high degree of accuracy sovthat uniform characteristics `from tube to tube may be ob tained. In accordance with my invention I provideY a thin sheet of imperforate vitreous insulating material and provide on said sheet by photographic processes a tacky discontinuous` surface to which very fine particlesof silicon carbide are made adherent, followed by firing the sheet and particles at an elevated temperature to provide recesses or bubbles distributed as a uniform array over the surface of the sheet. As disclosed in my original application, I may form apertures over the recessed or bubble area of the vitreous sheet by acid etching whereupon, for specific uses and in accordance with my invention, I lfill the apertures with metal without coating adjoinf ing surfaces of the sheet with conductive matter remaining afterthe sheet is ready for use. Alternatively, the apertures may be coated with' mosaic particles only over the internal-,surfaces or over the boundary areas thereof, therebyxformgtages of my invention will be apparent fromthe following description and with reference accompanying drawing wherein: y

Figure 1 shows a portion of a vitreousfoundag tion sheet partially prepared foruse in practicing my invention, and y v e 4Figures 2-7 show various stages of th'e manu-g facturing process in accordance with myinvenv-, tion.

It will be appreciated that ture made in accordance with my inventionuis useful in manyvtypes of electron discharge tubes, particularly of the television transmittingand image recreation types, and consequently, Izhave not shown in tube vto which it is applicable. For. example, the target structure may be utilized-in image tubes scanned by. a low velocity electron beam such as described in U. S. Patent 2,213,179, al-v though one modification thereof may beusedias a double-sided mosaic electrode as shownin U. S. Patent 2,213,178. In addition,l anelectrode made in accordance with my invention may'b'e used as an electron emission image control ,'elec trode such vas described in my copending, applicaf tion serial No. 463,o66, nieu' loctober 23 y1942, While the flnal'target electrodes asusediiifthe'se various tubes are somewhat different by reason of additional processing, my method` of'manu'- facture provides an electrode or electrodev fo dation suitable for such use with or without` ditional processing steps as disclosed moraparticularly hereinafter.

Referring to Figure l, the target foundation comprises a very thin initially imperforate'fouii dation sheet I of electrically insulating orjsernlinsulating material such as glass having afref sistance, for the particular applications referr to below, greater than 1011 ohm-centime rs. Preferably, an exceptionally thin homogeneous sheet of glass having the ldesired specificy resi-it ancel dependent upon its specific use and. being smooth andv of uniform thickness may` beus'ed. I have used glass known in the ai'tk as yCorning 705 glass with satisfactory results. Preferably, the target foundation sheet I has aninitial,thick1 -4 ness of from 0.001 to 0.005 inch and `may. be 'prof vided by `blowing a bubble of the desiredglass composition, they wall of the bubble thenbeliig sealed and flattened on an annular angeclsuplport 2, as described by VAlbcrtkRose in his of the drawing any particular typevf v adhesive and preferably of "voitie thin coating of a tacky substance. such as a very',

thin coating of rubber cement 3. The prerequisites of this coating are thatit;,-sho

that upon a subsequent removed such as by bakin perature. The thin coating may be formed of latex dissolved in a latex solsananet vent, and I have found the5cuiiiliiersziitl. -.1'.llbbel'-li1` cement known as Best-Test as supplied y, e: Union Rubber and Company, of

Y m saltata-anelli es v tvl devlopffthe l im s' hprrerrwoe fihezfwndatinlvj une silicon carbidei'n dan dinthe;

Another alternative method of preparing the foundation sheet I is shown in Figure 3 wherein the sheet I is coated directly with the photographic emulsion 4', this emulsion being rendered tacky for the purpose of attaching silicon carbide particles, thereby serving a dual purpose, namely, as a photographic emulsion and as the tacky 'coating 3. In this modified step of Vmy process, however, I use a photographic emulsion solution which when dry is inherently tacky so that the .y siliconcarbide may be distributed uniformly and become uniformly adherent to the emulsion layer as shown in Figure 3 at I0; for example, the silicon carbide particles may be ap- 'plied by depositing a quantity thereof on the emulsion 4', the excess particles being blown oil.' with a blast of air. Following the application of the silicon carbide particles, the emulsior. layer 4 is exposed to light, such as from the light source X shown in Figure 3, through a positive 6a of an electrolyticscreen and through the foundation sheet I inasmuch as the silicon carbide particles are relatively opaque rendering projection through the sheet I necessary. It will be noted that this exposure exposes minute halftone dot-like areas of the emulsion which is then developed in water tov remove the unexzposed emulsion.'V This development is preferably in hot water, approximately 50 C., the temperature being proportional to the time of exposure. Following this washing process, the foundation sheet i will have small discrete separated areas of the emulsion supporting the silicon carbide particles, these areas being separated by clear areas of the foundation sheet from which the emulsion and vthe silicon carbide particles have been removed.

It will be noted that in using either of the steps which I have described above the foundation sheet I' is provided with mutually separated piles of silicon carbide particles, separated from the foundation in the first instance bythe tacky rubber 111m 3, and in the second'instance-by individual areas of the photographic emulsion. 'Ihe preparedfoundation is then red or baked at a temperature slightly exceeding the softening point of the vitreous foundation. During the initial stages of this baking the rubber coating 3 or the remaining areas of the emulsion 4, as the case may be, vaporize and small bubbles II are formed in the vitreous foundation sheet I as shown in Figure 5. Preferably, this firing or baking step'is performed by placing the prepared foundation sheet in afurnace or oven at room temperature and heating the oven and sheet to a 'final temperature at which the foundation slightly softens. This temperature will depend upon the particular composition of the foundation sheet, although when using the 'I05`glass referred to above the bubbles II lbegin to form at a temperature around 775 C. Alternatively, using this same glass the prepared foundation may be inserted in an oven which has been heated previously to approximately 800 C., allowing the foundation to remain in the oven for 5 minutes following which it is removed from the oven and cooled. If glass other than Corning 705 is used, the required baking temperature may vary slightly from the above temperature and'I have found that a temperature at which the glass sticks and seals to the iron-nickel-cobalt alloy described by Scott in his U. S. Patent 1,942,260 is a satisfactory temperature for forming the bubbles II. I have been unable to discern any difference in the bubbles whether or not use is 75 made of the rubber nlm intermediate the emulrepeated several' times.

sian andthe glass. or whether the pnotcgrapmc emulsion alone is used, the bubbles appearing to be'substantiallythe same size and configuration notwithstanding which alternative step is used.`

Following the firing operation I immerse the sheet in s, hydrofluoric acid solution which loosens and vdissolves the silicon carbide particles las well as a 4portionI ofthe glass foundation. Consequently, the thickness' of the original glass foundation sheet is chosen to allow for this step and consequent reduction in sheet thickness. For this step I prefer to use an aqueousl solution of ten parts of water to one part `of concentrated hydrofiuoric acid. The foundation may be` -immersed in this solution vfor a time sufficient" to removel the silicon carbide particles but msnm-- cient to open the bubbles to the lower side of the fundation sheet leaving forate form as shown in Figure 5. 'Such a foundati'on' is of particular advantage inl my secondmentioned copending application wherein the lower surfaces ofthe bubbles I l are provided with a red sensitive photo-electric coating, the upper surface of the sheet, that is around the recesses or bubbles, being'coated with a blue sensitive photo-electric coating. Alternatively, the foundation shown in Figure 5 may beailowed to re' main in the acid solution for a time sufiicient to open the bubbles on the lower side to provide the structure shown in Figure 6 wherein the bubbles have formed apertures I2 extending completelyA through'thev foundation sheet I. Such a'struc-v ture isyuseful when coated .on one lside with a mosaic of '.photosensitive elements forv use i'n a tube such a's-shown by U. S. Patent'vv 2,213,179. Further in accordance with my invention, the apertures I2 shownlin Figure 6 maybe filled with metal plugs i3 sidedtype such as shown in Figure '7. To provide this type 0f target I lay a thin lacqueri'llm over one surface of the foundation following the acid treatment and following the opening of the apertures I! through the foundation. Such a 'thin lacquer film may beproduced of lacquer to spread over the surface offan immiscibleliquid such as water. Theiacquer, fol'- the sheet 4in'its imperf conducting film, if of graphite, is removed by useA of a solvent fory the graphite binder, or by dissolving-in sodium hydroxide if the film is made of aluminum.

Alternatively, the metal plugs I3 may be formed in the apertures of the foundation by a somewhat Y modified process wherein the thin lacquer. film,

as previously described, is laid upon the apertured foundation Vfollowed by the application of' graphitedirectiy thereto for the formation of a con.

ductive film. n I prefer to mix graphite with wood alcoholgto` a relativelythlnconsistency and brush this mixture on'the lacquer film. The wood alcohol ,serves as a partial solvent to wet the lacquer, forming electrically conductive paths through the lacquer-1 film to the graphite coating. After thisfcoating is contact with a mercury bath and pour the plating solution over the bath to fill the apertures with the plating solution.. The mercury bathl and graphite coating metal plugs in thejfoundation` I.

From they above, it will'be appreciated that If haveprovided accurate means for distributing minute piles of' siliconk carbide over the surface toprovide a target of the doubleby allowing a dropv lowing spreading, dries very rapidly and the thin.

filmmaybelplaced on-the foundation I by im-A mersing the'1 foundation in the water lpriorto. formation ofthe film and withdrawing the founof vafthin 'glassfoundationiand using these piles toprovide underflthe influence of heating a cor-,-

` responding number of bubbles o r apertures distributed in the same order over the foundation sheet and likewise a new method of developing metal plugsA within'the apertures thus formed. Furthermore; while I have disclosed only three specific types of electron discharge tubes in which my electrode structure is applicable, it will Vbe appreciated that the structure may be used in l `other tube types and for other applications than` the specified ytelevisiony transmitting and imageV tube-,use without departing from the scope of the:

appended claims.

I claim:V

1. Themethod of manufacturing a foundation for an electrode structure comprising forming dation thereby lifting the lacquer film upon the aperturedfoundation and from .the surface .ofy the -1 water. The apertures are then filled with, a .11%-

gelatin "solution from the' opposite .sidefof the.l

, foundationfrom the lacquer.filliilv vThis'fillingpfl the aperturesmaybe performed by'first" pouring the gelatin solutionupon the foundation and vvthen draining'` and u Ithe'n dissolve; the lac.- quer vfilm by immersingthe foundation in acetone orothen solvent -for the lacquer-and replace the drying, tl'iese alternate steps being temperature approximating the softening temfilm with` a conducting :layer such as a film of y graphite or aluminum. -If graphite is used, it may lacquer?. Orifa/metal such' as aluminum is used',

it-fmay f be vaporized andl conden'sedon this sur- Following the application of the conduc- Abespreadl on the surface following removal ofthe discrete separated adhesive areas on a glass foundation, distributing .finer particles of silicon carbide .over'said adhesive areas and heating said foundation Vto .a temperature suiiicient to` soften said .glass and formj bubbles in said foundation underlying said adhesiveareas by said gas.

. 2.' The method of manufacturing a foundation for an electrode structure comprising distrlbut Y irigvfiifie `particles ofsilicon-carbide over separated adhesive'areas cna glass foundation, and heating said foundation and said particles to a perature of said glass to form bubbles underlying said ,fine'particles of refractory material by said gas and' .removing said particles to expose said bubbles. f'

3. rThemethcd of` manufacturing an electrode foundation structure comprising forming discrete uniformly separated adhesive areas on a glass foundation, covering each of said areas rwith a quantity of fine particles of silicon carbide, heat-` ingsaid glass foundation bearing said particlesk i to vva temperature approximating the softening point of said glass to form bubbles in said glass underlying saidparticles and removing said particles to ex-pose a. regular array of bubbles posidry I place the graphite in.

thenV serve as Ia cathode in thev plating operation, forming the mutuallyseparated 7 tioned in accordance with the uniform Separation of said areas.

4. The method ofmanufacturing an electrode foundation structure comprising the steps of coating a thin glass sheet with an adhesive layer, coatingsaid layer with a photographic emulsion. exposing portions of said emulsion to light through a photographic negative thereby shielding uniformly separated point-like areas of said emulsion from light, developing and washing said emulsion to expose to view uniformly separated point-like areas of .said adhesive, coating said point-like adhesive areas with particles of silicon carbide and baking said foundation to develop bubbles therein over said point-like areas.

5.` The method of manufacturing' an electrode foundation structure comprising the steps of forming an adhesive coating on a thin glass foundation, covering said coating with al mask of photographic emulsion, exposing and developing predetermined portions of said emulsion to unmask portions of said coating, covering said portions of said coating with fine particles of silicon carbide, heating the prepared foundation to a temperature at which the glass softens and at which bubbles are formed therein, and immersing said foundation in an acid to remove said particles'of silicon carbide.

6. The method of manufacturing a target electrode member comprising a thin sheet of glass comprising coating said sheet of glass with an adhesive illm of photographic emulsion of the potassium dichromate type. covering said iiim with ine particles of silicon carbide, exposing portions ,of said nlm to light, removing the por tions thereof not exposed together with the overlyingsilicon carbide particles, heating the prepared sheet of glass to develop bubbles in said glass sheet underlying the remaining particles of silicon carbide and removing the remaining particles of silicon carbide to expose said bubbles at the surface of said sheet of glass.

7. The method of manufacturing 'an electrode foundation structure comprising coating a thin sheet of glass having a softening point below 800 C. with a photographic emulsion lm containing an adhesive substance. coating said film with ine particles of silicon carbide, photographically exposing said emulsion through said sheet of glass over separated point-like areas. removing the unexposed portions of said emulsion while retaining said particles onthe exposed portions thereof and heating the prepared sheet of glass to a softening temperature to develop bubbles underlying the particles of silicon carbide retained on the exposed portions of said emulsion illm.

. HAROLD B. LAW. v 

